If you're talking about the catapult – the one that breaches walls, not the ballista – then the "sulfur rain" ability, which is essential for obtaining the special ability "pure rage," grants 3 shots. Plus, the Ring of the Magi provides one additional shot.

Of course, I'm talking about the catapult, and I perfectly understand how it can fire 4 times. :)
What surprised me was something else:

first destroying the catapult (then he [Grobok] hangs around near the castle walls).

I didn't understand how it was possible to hide behind the castle walls after destroying the catapult, if it moves before all the units capable of destroying it and immediately creates a breach in the walls, and sometimes even several breaches. Or does Grobok have different specializations each time?

P.S. As for the ancient Greek gods, it's not befitting for them to crush lesser beings; they fought the Titans once, and that's enough. That's why they created Heracles, Perseus, and other Castor and Pollux types. :)
By the way, all these heroes were also demigods and found a place in the pantheon (they were, after all, the children of Zeus himself).